1. Field of the Invention
The present invention relates to a zero-delay queuing method and system, and more particularly, to a zero-delay queuing method and system in which a Class-Based Queuing (CBQ) scheduler transfers specific traffic requiring real-time transfer without delay and also performs queuing through first to third phases to ensure a uniform Committed Rate (CR) and Peak Rate (PR) even when traffic is very congested.
2. Description of the Related Art
In a routing system supporting interfaces having various bandwidths, a bottleneck is caused when traffic is transferred from an input interface having a large bandwidth to an output interface having a small bandwidth. In this case, a Quality of Service (QoS) scheduler selectively drops a packet at the bottleneck point or transfers packets according to a queuing mechanism, thereby adjusting the entire flow of traffic.
When the flow of traffic is adjusted by selectively dropping a packet, there is no delay caused by packet buffering. The packet loss, however, may result in abnormal transfer of information.
Meanwhile, when a packet is transferred according to a queuing mechanism, the QoS scheduler performs a shaping function to uniformly transfer traffic without dropping the packet. According to the shaping function, an overflowing packet is buffered and transferred to adjust a bandwidth of transferred packets. When performing the shaping function, the QoS scheduler buffers traffic exceeding a reference value of a bandwidth allocated to each class to save the information of the traffic, and thus reduction of traffic loss is possible. Packets, however, are buffered and then transferred, and thus causing transfer delay.
A CBQ (Class Based Queuing) scheduler performs queuing based on a packet class. In order to support CBQ scheduling when traffic is very congested in an interface having a small bandwidth, e.g., T1/E1, T3 or Ethernet, a scheduler operation period is required in consideration of the CBQ scheduler's operation overhead. Here, during a period of several milliseconds in which the scheduler operates, packets must wait to be transferred in respective class queues, which results in queuing of traffic or scheduling delay. In other words, the CBQ scheduler can somewhat reduce transfer delay of packets but cannot prevent basic transfer delay of packets.
Currently, there is no method of transferring specific traffic, for example, traffic requiring real-time transfer, without queuing or scheduling delay in a CBQ scheduler. Meanwhile, when traffic is very congested in the corresponding interface, there is no method of transferring the traffic which should be transferred without queuing or scheduling delay ensuring a CR (Committed Rate) and a PR (Peak Rate). In this case, the CR (Committed Rate) means a uniform transfer quantity for the traffic. And, the PR can be ensured when there is available bandwidth in the interface during a scheduling period.
Therefore, CBQ schedulers require a zero-delay queuing mechanism that may transfer a packet without transfer delay, and furthermore, may transfer a packet while ensuring a uniform CR and PR of traffic even when the traffic is very congested.